1. Field of the Invention
The present invention relates to an image display device having a function of detecting a defect in a plurality of light-emitting diodes, a drive circuit device, such as a driver IC, and a defect detection method of a light-emitting diode.
2. Description of the Related Art
In a variety of indoor and outdoor event places, indoor and outdoor stadiums and other sport facilities, an image display device for video and information using an LED as an display element (hereinafter, referred to as an LED display) is used for displaying sport live, live telecast and advertisement. In an LED display, a display cell is composed of unit pixels of m lines by n columns. There are monochrome display and color display. In the case of color display, a unit pixel is composed of three LEDs: red (R), green (G) and blue (B).
The LED display used for various uses explained above is generally very large and placed at a high position.
When conducting a test before shipping by operating an LED in a state of being mounted on a display panel or when operating the display in a state of being installed at the use place, electric connection in the LED becomes nearly short-circuited or open due to dusts, temperature and temperature changes, etc. in some cases. In these cases, an LED in a defective condition shows a state of having excessively higher or lower luminance than that of good ones or, furthermore, not illuminating at all, which leads to a deterioration of image quality of the display. A display is arranged with a large number of LEDs and it is possible to specify a defective LED from the luminance. However, in the case of a large-scale LED display used in the above objects, it is very difficult to specify a defective LED by difference of luminance at the time of shipping test because of the large number of the LEDs. Furthermore, when exchanging a defective LED after installment in the use place, judgment of defective or good luminance has to be made, for example, in a state of directly receiving a sun light, so that there are some cases where judgment of defect from good is difficult under a use environment as such. Furthermore, when installed at a high position, a large amount of labor and high maintenance costs are required for exchanging a defective LED.
From the above reasons, there has been a demand for a method of electrically detecting a defective LED or an LED with a high probability of becoming defective before shipping or after installment at the use place.